As demonstrated so terribly by recent events, anthrax poses a deadly threat as a biological weapon of terrorism and warfare. Systemic intoxication by anthrax toxins is virtually always fatal but effective treatment is not available. The goal of this application is the development of potent inhibitors that prevent the assembly of anthrax toxin complexes. Anthrax toxins are responsible for the major symptoms of the disease. The toxins consist of a host receptor-binding protein termed protective antigen (PA) and two enzymes termed lethal factor (LF) and edema factor (EF). These proteins are released from Bacillus anthracis as nontoxic monomers. They diffuse to the surface of host cells and assemble into two types of toxic protein complexes, lethal toxin (LF+PA) and edema toxin (EF+PA). PA is the necessary vehicle that transports LF and EF from the cell surface to the cytosol where LF and EF exert their cytotoxic effects. Hence, inhibitors that prevent the binding of LF or EF to PA should provide an effective antitoxic therapy against anthrax. Previously, we have identified several peptides that bind PA weakly and inhibit the interactions of LF or EF with PA. We hypothesize that, through cooperative interactions, multivalent inhibitors (MVIs), in which multiple copies of a peptide are coupled to a carrier molecule, will display significantly enhanced inhibitory effects. In our preliminary study, we have synthesized several dextran-based MVIs that show higher inhibitory activities than peptides alone. We propose to develop optimized MVIs based on biocompatible, nontoxic, linear polymers and cyclic oligomers as carriers. Aim 1. To optimize MVIs based on dextran and pectin carriers. Aim 2. To explore MVIs based on polyglutamate backbones. Aim 3. To design and develop heptavalent "crown" MVIs based on (-cyclodextrin cores. In Aims 1 and 2, we plan to synthesize a series of peptide-polymer conjugates in which the peptide-to-backbone ratio and the molecular size of the backbone are systematically varied. In Aim 3, we will assist the design of crown inhibitors by computational modeling. We will test all MVIs in our established inhibition assays and the most active MVIs in two rat intoxication models. Potent inhibitors developed in this study can help to protect us from deadly anthrax disease and fight the threat of anthrax bioterrorism.